CN108630927B - Preparation method of lithium manganese iron phosphate coated lithium-rich manganese-based positive electrode material and lithium battery - Google Patents

Preparation method of lithium manganese iron phosphate coated lithium-rich manganese-based positive electrode material and lithium battery Download PDF

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CN108630927B
CN108630927B CN201810439462.1A CN201810439462A CN108630927B CN 108630927 B CN108630927 B CN 108630927B CN 201810439462 A CN201810439462 A CN 201810439462A CN 108630927 B CN108630927 B CN 108630927B
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manganese
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CN108630927A (en
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白培锋
张海林
李艳
计结胜
王慧景
黄海军
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Nanjing Kanai New Energy Technology Development Co ltd
Shanghai Cenat New Energy Co Ltd
Guangxi Cenat New Energy Co Ltd
Jiangsu Cenat New Energy Co Ltd
Nanchang Cenat New Energy Co Ltd
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Nanjing Kanai New Energy Technology Development Co ltd
Shanghai Cenat New Energy Co Ltd
Guangxi Cenat New Energy Co Ltd
Jiangsu Cenat New Energy Co Ltd
Nanchang Cenat New Energy Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a preparation method of a lithium-rich manganese-based anode material coated by lithium manganese iron phosphate, which comprises the steps of preparing an organic phase; preparing a water phase, replacing by hydrothermal back extraction, and washing and drying a product; the preparation method of the water phase comprises the following steps: weighing a lithium source with a stoichiometric ratio, adding deionized water to prepare a lithium ion solution with the concentration of 0.1-1 mol/L, and then adding 1.0-4.0 mol/L H3PO4Adjusting the pH of the solution to 5-8 by ammonia water, adding 0.5-2 g of ascorbic acid, and finally adding Li rich in lithium and manganese1.2Mn0.54Ni0.13Co0.13O2The materials are stirred evenly to obtain LiH containing the material rich in lithium and manganese2PO4A solution; and in the hydrothermal back-extraction coating step, a layer of uniform lithium iron manganese phosphate is generated on the surface of the lithium-manganese-rich material by using a hydrothermal back-extraction method. The lithium battery formed based on the cathode material is also disclosed, and the battery cyclicity is obviously improved. The preparation scheme has the advantages of low reaction temperature, short time, less energy consumption, recyclable organic solvent, reduced consumption of chemicals, no environmental pollution problem, simple process flow and easy industrialization.

Description

Preparation method of lithium manganese iron phosphate coated lithium-rich manganese-based positive electrode material and lithium battery
Technical Field
The invention belongs to the field of electrochemical materials, and particularly relates to a lithium battery positive electrode material technology.
Background
In recent years, lithium ion batteries have attracted attention because they have seen unprecedented application prospects in Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), and the like. Lithium-rich manganese-based positive electrode material xLi2MnO3.(1－x)LiMO2(M ═ one or more of Ni, Co, and Mn) has attracted much attention because of its high energy density, low cost, and the like. However, poor cycling performance has greatly limited the commercial development of lithium-rich manganese-based materials.
In order to solve the above problems, a great deal of research and development is carried out, mainly including surface coating, bulk phase doping and surface treatment. Wherein, the surface coating is a simple and effective modification methodThe coating material can effectively prevent the electrolyte from corroding the surface of the lithium-rich material, optimize the interface reaction electrochemistry, reduce the interface reaction electrochemistry resistance and improve the cycling stability of the material. The main coating materials are: MgO, Al2O3，AlPO4、MgPO4，Li4Ti12O5、LiMnPO4、LiNiPO4。
The selection of a proper coating material and a proper coating method are particularly important for improving the electrochemical performance of the lithium-rich manganese-based cathode material.
For example, chinese patent application publication No. CN106450211A (application No. CN201610968394.9) discloses a surface-coated composite lithium-rich manganese-based cathode material and a method for preparing the same, in which a solid-phase method is used to coat lithium-rich manganese-based material with lithium iron manganese phosphate, but this method cannot effectively control the coating layer, and is likely to cause a phenomenon of non-uniform coating, which finally leads to a larger polarization of the material.
Therefore, the problem to be solved in the art is to provide a scheme capable of effectively improving the electrochemical performance of the lithium-rich manganese-based cathode material.
Disclosure of Invention
Aiming at the problems existing in the production process of the existing lithium-rich manganese-based cathode material, a new production scheme of the lithium-rich manganese-based cathode material is needed.
Therefore, the invention aims to solve the problem of providing a preparation method of a lithium-rich manganese-based positive electrode material coated with lithium iron manganese phosphate, so as to overcome the defects in the prior art; and further provides a corresponding lithium battery on the basis.
In order to solve the above problems, the preparation method of the lithium iron manganese phosphate coated lithium-rich manganese-based positive electrode material provided by the invention comprises the following steps:
preparing an organic phase;
a step of preparing an aqueous phase, the step comprising:
weighing a lithium source with a stoichiometric ratio, adding deionized water to prepare a lithium ion solution with the concentration of 0.1-1 mol/L, and then adding 1.0-4.0 mol/L H3PO4The solution is prepared by mixing a solvent and a solvent,adjusting the pH value of the solution to 5-8 by ammonia water, adding 0.5-2 g of ascorbic acid, and finally adding Li rich in lithium and manganese1.2Mn0.54Ni0.13Co0.13O2The materials are stirred evenly to obtain LiH containing the material rich in lithium and manganese2PO4A solution;
a hydrothermal back extraction coating step, wherein a layer of uniform lithium manganese iron phosphate is generated on the surface of the lithium manganese rich material by using the prepared organic phase and the prepared aqueous phase to perform a hydrothermal back extraction method;
and (5) washing and drying the product.
Further, the preparation step of the organic phase comprises mixing an extracting agent and a diluent, adding ammonia water to adjust the pH value, adding the mixed metal ion solution, continuously stirring uniformly, separating the organic phase by using a separating funnel, and washing by using deionized water to obtain the metal ion loaded organic phase.
Further, the extracting agent is any one of naphthenic acid and tributyl phosphate, and the diluent is kerosene.
Further, the mixed metal ion solution is Fe2+，Mn2+ in the proportion of c (Fe)2+)：(Mn2 +)＝(1-9)：1。
Further, in the step of preparing the aqueous phase, the amount of the weighed lithium source substance is 3% -5% of the amount of the added lithium-manganese-rich material substance.
Further, in the step of preparing the aqueous phase, a lithium source is mixed with H3PO4The mass ratio of (1): 1.
further, the lithium source is any one of lithium hydroxide, lithium carbonate and lithium acetate.
Further, the product washing and drying step comprises the following steps: and (3) separating solid from liquid by a centrifugal pump, recycling the organic phase, washing the solid with distilled water and absolute ethyl alcohol for three to four times, and drying at 60-85 ℃ for 2-5 h to obtain the lithium-rich manganese-based anode material coated by the lithium manganese iron phosphate.
The lithium battery provided by the invention comprises a positive electrode, a negative electrode, electrolyte and a diaphragm, wherein the positive electrode is made of the lithium-rich manganese-based positive electrode material coated with the lithium iron manganese phosphate formed by the preparation method.
The hydrothermal back extraction method adopted by the preparation method provided by the invention is a liquid phase coating method, a uniform coating layer can be generated (namely a layer of uniform lithium manganese iron phosphate is generated on the surface of the lithium manganese material by the hydrothermal back extraction method), compared with the solid phase coating method, the thickness and the shape of the solution are controllable, and the cycle performance of the coated product is obviously improved.
Moreover, the preparation method has the advantages of low reaction temperature, short time, low energy consumption, wide raw material source, environmental friendliness, simple process and easy industrialization.
Moreover, the preparation method can reduce the purity of the raw materials and reduce the cost through organic extraction.
Drawings
The invention is further described below in conjunction with the appended drawings and the detailed description.
FIG. 1 is a diagram of the charge-discharge cycle performance of a lithium battery prepared from the positive electrode material in the example of the present invention.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained below by combining the specific drawings.
The scheme mainly comprises the following basic steps of preparing the lithium-rich manganese-based positive electrode material coated by the lithium iron manganese phosphate:
preparing an organic phase;
the preparation method of the organic phase mainly comprises the steps of adding an extracting agent and a diluent into a beaker according to the volume ratio of (1-3) to 1, uniformly mixing, then adding ammonia water with the corresponding volume ratio to adjust the pH value, finally adding 0.1-0.8 mol/L of mixed metal ion solution, continuously and uniformly stirring, separating out the organic phase by using a separating funnel, and washing by using deionized water to obtain the metal ion loaded organic phase.
The extractant is any one of naphthenic acid and tributyl phosphate, and the diluent matched with the extractant is kerosene. Kerosene is used as a diluent, does not react with the selected extracting agent, can play a role in diluting the extracting agent, and is mixed for use, so that the extraction effect is better.
The mixed metal ion solution in the step is Fe2+，Mn2+The mixed solution of (1) in the proportion of c (Fe)2+)：(Mn2+)＝(1-9)：1。
And Fe in the mixed metal ion solution2+、Mn2+The salt is any one of sulfate, acetate and nitrate. By adopting the mixed ions, lithium manganese iron phosphate coated on the surface of the lithium-rich material can be effectively generated through reaction.
A water phase preparation step;
the method mainly comprises the following steps:
firstly, weighing a lithium source with a stoichiometric ratio in a beaker, wherein the amount of substances of the lithium source is 3% -5% of the amount of substances of the added lithium-rich manganese material, so that a coating layer with a proper thickness can be formed, and the phenomenon that the material performance is influenced by too much or too little coating is avoided;
then, a certain volume of deionized water is added to prepare a lithium ion solution with the concentration of 0.1-1 mol/L, and then a certain volume of 1.0-4.0 mol/L H is added3PO4Solution of lithium source and H3PO4The mass ratio of (1): 1, whereby LiH can be reacted to form2PO4；
Then, adjusting the pH value of the solution to 5-8 by ammonia water, adding 0.5-2 g of ascorbic acid, and finally adding Li rich in lithium and manganese1.2Mn0.54Ni0.13Co0.13O2The materials are stirred evenly to obtain LiH containing the material rich in lithium and manganese2PO4And (3) solution.
The lithium source herein is any one of lithium hydroxide, lithium carbonate, or lithium acetate.
The aqueous phase prepared by the method can effectively synthesize the coating lithium manganese iron phosphate material
A hydrothermal back extraction coating process;
the step of using the prepared organic phase and the prepared water phase to carry out a hydrothermal back extraction method to generate a layer of uniform lithium manganese iron phosphate on the surface of the lithium manganese material, namely, the hydrothermal back extraction method is used for uniformly coating the lithium manganese iron phosphate on the surface of the lithium manganese material.
Specifically, the organic phase and the water phase are added into a reaction kettle according to the volume ratio of 1 (1-3), the temperature is heated to 150-240 ℃ under magnetic stirring, the heating is stopped after the reaction is carried out for 30-180 minutes, and the stirring is continued until the temperature is cooled to the room temperature.
And (3) washing and drying the product, namely separating solid from liquid by a centrifugal pump, recycling an organic phase, washing the solid with distilled water and absolute ethyl alcohol for three to four times, and drying at the temperature of 60-85 ℃ for 2-5 h to obtain the lithium-rich manganese-based anode material coated by the lithium iron manganese phosphate.
The preparation scheme of the lithium-rich manganese-based positive electrode material coated with lithium iron manganese phosphate is further described below by using some specific examples.
Example 1
The process for preparing the lithium-rich manganese-based positive electrode material coated with lithium manganese iron phosphate in the embodiment is as follows:
1) preparing an organic phase;
sequentially adding 30mL of industrial grade tributyl phosphate and 10mL of kerosene according to the volume ratio of 1:1 in a beaker, uniformly mixing under stirring, then adding 8mL of ammonia water for saponification, adjusting the pH value to 7, and finally adding 200mL of 0.1mol/L mixed metal ion solution, wherein the mixed metal ion solution is ferrous sulfate and manganese sulfate according to the molar ratio of 0.9: 0.1, continuously stirring for 0.5h, pouring into a separating funnel, standing for 10 minutes, separating the liquid into two phases, separating, and washing with deionized water for two to three times to obtain 40mL of metal ion-loaded organic phase.
2) Preparing an aqueous phase;
0.4788g of LiOH was weighed into a beaker, 80mL of deionized water was added, and after all the solids had dissolved, 6.67mL of H was added3PO4(concentration: 3mol/L), after stirring well, adjusting pH to 6 with ammonia water, then adding 0.6g ascorbic acid, 100g lithium-rich material Li in sequence1.2Mn0.54Ni0.13Co0.13O2And (4) carrying out ultrasonic treatment for 30min, so that the solid lithium-rich material is uniformly dispersed in the water.
3) A hydrothermal back extraction substitution process;
adding the organic phase in the step 1) and the water phase in the step 2) into the same reaction kettle, heating to 180 ℃ under magnetic stirring, heating at a rate of 3 ℃/min, reacting at 180 ℃ for 90 minutes, stopping heating, and continuing stirring until the temperature is cooled to room temperature.
4) Washing and drying the product;
after the reaction is finished, solid-liquid separation is carried out through a centrifugal pump, the organic phase is recycled, the solid is washed for four to five times by using distilled water and absolute ethyl alcohol, and the solid is dried for 3 hours at the temperature of 85 ℃ to obtain the lithium manganese base-rich anode material LiFe coated by the lithium iron manganese oxide0.9Mn0.1PO4@Li1.2Mn0.54Ni0.13Co0.13O2。
In addition, the reaction principle for preparing the lithium-rich manganese-based positive electrode material coated with lithium manganese iron phosphate is as follows:
(1) preparing an organic phase;
the organic phase loaded with ferrous ions is prepared by adopting a traditional solvent extraction technology, and the principle is as follows: 9Mn2++Fe2+(aq)+20(RCOOH)2(org)→Fe(RCOO)2(org)+9Mn(RCOO)2(org)+2H+(aq)；
Wherein (RCOOH)2Represents tributyl phosphate.
(2) Preparing an aqueous phase;
LiOH+H3PO4→LiH2PO4(aq)+H2O；
because the lithium-rich manganese material is added into the water phase, the water phase contains the lithium-rich manganese material Li1.2Mn0.54Ni0.13Co0.13O2LiH of (2)2PO4A liquid.
(3) The hydrothermal stripping is Fe2+And Mn2+Organic phase extraction to aqueous phase replacement of H +:
Figure GDA0001770836960000051
when the reaction (3) occurs, the extraction agent tributyl phosphate is released again and can be reused after separation. Formation of LiFe0.1Mn0.9PO4(aq) subsequently nucleating on the surface of the lithium-rich manganese material and generating a coating layer:
Figure GDA0001770836960000061
the coating method can coat a layer of uniform lithium iron manganese phosphate material on the surface of the lithium manganese rich material, and has the advantages of controllable thickness, simple preparation process, short time, rich raw materials and easy industrialization.
Example 2
The process for preparing the lithium-rich manganese-based positive electrode material coated with lithium manganese iron phosphate in the embodiment is as follows:
1) preparing an organic phase;
in a beaker, the volume ratio of 3: 2 adding 30mL of industrial grade tributyl phosphate and 20mL of isooctanol in sequence, uniformly mixing under magnetic stirring, adding 8mL of ammonia water with the volume ratio of 1:1, adjusting the pH to 8, and finally adding 200mL of 0.3mol/L mixed metal ion solution in which c (Fe) is contained2+)：c(Mn2+) 0.8: 0.2, stirring for 20 minutes, pouring into a separating funnel, standing for separating, separating an organic phase, and washing with deionized water for two to three times to obtain the metal ion loaded organic phase.
2) Preparing an aqueous phase;
1.3464g of LiOH was weighed into 100mL of deionized water, and after the solids had dissolved completely, 20mL of H was added3PO4(concentration: 3mol/L), after stirring well, adjusting pH to 7 with ammonia water, then adding 1.8g ascorbic acid, 300g lithium-rich material Li in sequence1.2Mn0.54Ni0.13Co0.13O2And (5) carrying out ultrasonic treatment for 30 min.
3) Hydrothermal stripping substitution process
Introducing the organic phase in the step 1) and the water phase in the step 2) into a high-pressure reaction kettle according to the volume ratio of 2:1, heating to 180 ℃ under magnetic stirring, stopping heating after reacting for 90 minutes, and continuing magnetic stirring until the reaction temperature is reduced to room temperature.
4) Processing a product;
after the reaction is finished, the solid and the liquid are separated,the organic phase is recycled, the solid is washed by distilled water and absolute ethyl alcohol for three to four times and dried for 5 hours at the temperature of 85 ℃, and the lithium iron manganese oxide coated lithium-rich manganese-based anode material LiFe can be obtained0.8Mn0.2PO4@Li1.2Mn0.54Ni0.13Co0.13O2。
Example 3
The process for preparing the lithium-rich manganese-based positive electrode material coated with lithium manganese iron phosphate in the embodiment is as follows:
1) preparing an organic phase;
adding 30mL of industrial grade tributyl phosphate and 10mL of kerosene according to the volume ratio of 3:1 into a beaker, uniformly mixing under magnetic stirring, adding 7mL of ammonia water with the volume ratio of 1:1, adjusting the pH value to 7, and finally adding 200mL of 0.2mol/L mixed metal ion solution, wherein c (Fe) in the mixed metal ion solution is mixed2+)：c(Mn2+) 0.5: and 0.5, continuously stirring for 0.5h, pouring into a separating funnel, standing for separating, separating an organic phase, and washing twice with deionized water to obtain the metal ion loaded organic phase.
2) Preparing an aqueous phase;
0.9576g of LiOH was weighed out, 120mL of deionized water was added, and after the solid had dissolved completely, 13mL of H was added3PO4(concentration: 3mol/L), after stirring well, adjusting pH to 7 with ammonia water, then adding 1.2g ascorbic acid, 200g lithium-rich material Li in sequence1.2Mn0.54Ni0.13Co0.13O2And (5) carrying out ultrasonic treatment for 30 min.
3) A hydrothermal back extraction substitution process;
introducing the organic phase in the step 1) and the water phase in the step 2) into a high-pressure reaction kettle according to the volume ratio of 3:1, heating to 230 ℃ under magnetic stirring, stopping heating after reacting for 45 minutes, and stirring until the temperature is reduced to room temperature.
4) Processing a product;
after the reaction is finished, solid-liquid separation is carried out through a centrifugal pump, the organic phase is recycled, the solid is sequentially washed for three to four times with distilled water and absolute ethyl alcohol, and the solid is dried for 3 hours at 85 ℃ to obtain the lithium manganese iron phosphate coated lithium-rich manganese-based anode material LiFe0.5Mn0.5PO4@Li1.2Mn0.54Ni0.13Co0.13O2。
Referring to fig. 1, a graph of the charge and discharge cycle performance obtained by testing a lithium ion battery formed by coating a lithium-rich manganese-based cathode material with lithium iron manganese phosphate prepared based on the above example is shown. As can be seen from the figure, the lithium ion battery prepared from the lithium manganese oxide coated lithium-rich manganese-based cathode material prepared by the preparation method has excellent cycle performance.
The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (6)

1. The preparation method of the lithium-rich manganese-based positive electrode material coated by the lithium iron manganese phosphate is characterized by comprising the following steps of:
an organic phase preparation step comprising:
mixing an extracting agent and a diluent, adding ammonia water to adjust the pH value, adding 0.1-0.8 mol/L of mixed metal ion solution, continuously stirring uniformly, separating an organic phase by using a separating funnel, and washing by using deionized water to obtain a metal ion loaded organic phase;
a step of preparing an aqueous phase, the step comprising:
weighing a lithium source with a stoichiometric ratio, adding deionized water to prepare a lithium ion solution with the concentration of 0.1-1 mol/L, and then adding 1.0-4.0 mol/L H3PO4Adjusting the pH of the solution to 5-8 by ammonia water, adding 0.5-2 g of ascorbic acid, and finally adding Li rich in lithium and manganese1.2Mn0.54Ni0.13Co0.13O2The materials are stirred evenly to obtain LiH containing the material rich in lithium and manganese2PO4Solutions of；
A hydrothermal back extraction coating step, wherein a layer of uniform lithium manganese iron phosphate is generated on the surface of the lithium manganese rich material by using the prepared organic phase and the prepared aqueous phase to perform a hydrothermal back extraction method; adding the organic phase and the water phase into a reaction kettle according to the volume ratio of 1 (1-3), heating to 150-240 ℃ under magnetic stirring, reacting for 30-180 minutes, stopping heating, and continuing stirring until the temperature is cooled to room temperature;
and (5) washing and drying the product.
2. The method of claim 1, wherein the extractant is any one of naphthenic acid and tributyl phosphate, and the diluent is kerosene.
3. The method of claim 2, wherein the mixed metal ion solution is Fe2+，Mn2+The mixed solution of (1) in the proportion of c (Fe)2+)：(Mn2+)＝(1-9)：1。
4. The production method according to claim 1, wherein the lithium source is any one of lithium hydroxide, lithium carbonate, and lithium acetate.
5. The method of claim 1, wherein the product washing and drying step comprises: and (3) separating solid from liquid by a centrifugal pump, recycling the organic phase, washing the solid with distilled water and absolute ethyl alcohol for three to four times, and drying at 60-85 ℃ for 2-5 h to obtain the lithium-rich manganese-based anode material coated by the lithium manganese iron phosphate.
6. The lithium battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm, and is characterized in that the positive electrode is made of the lithium-rich manganese-based positive electrode material coated with the lithium iron manganese phosphate formed by the preparation method of any one of claims 1 to 5.
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